1. Field of the Disclosure
The present disclosure relates generally to formation testing apparatus and methods.
2. Description of the Related Art
Pressure-volume tests are typically performed downhole to estimate formation properties and the condition of reservoirs. To perform such tests, a downhole tool is conveyed into a wellbore. A small amount (1 cc-10 cc) of the fluid from the formation is withdrawn generally using a piston. The pressure drop at the point from which the fluid is being withdrawn starts as the drawdown starts. The total amount of the pressure drop generally depends upon the properties of the formation, such as the type of rock, permeability, etc., and the properties of the formation fluid, such as the viscosity, etc., of the fluid. In such tests, the total drop in pressure is typically not controlled and can vary substantially from one test to another and from one formation to another. After the drawdown cycle, the pressure is allowed to build-up until it reaches a stable level. The length of time it takes for the pressure to build-up to the formation pressure level (the “build-up time”) depends upon the type of the formation. For example, the build-up time for tight formations can be form several minutes to hours. Typically, three draw-down and build-up tests are performed to determine the reservoir condition. Therefore, drawing preselected volumes of fluid during draw-downs can lead to excessive build-up times, especially in tight formations, which can be relatively expensive, due to idle rig and personnel time.
Therefore, there is a need for an improved apparatus and methods for formation testing applications.